And the Lord remembered Sarah (Gen. 21:1). Scripture says elsewhere in allusion to this verse: Then the nations that are left round about shall know that I, the Lord, have builded the stricken places, and have planted that which was desolate: I, the Lord, have spoken it, and I will do it (Ezek. 36:36).

The nations shall know refers to the women who taunted Sarah by calling her a barren woman. I, the Lord, have builded the stricken places indicates that she was stricken with old age, as it is said: And Abraham and Sarah were old, and well stricken with age (Gen. 18:11). Have planted that which is desolate refers to her remark: After I am waxed old, shall I have pleasure? (ibid., v. 12). And I, the Lord, have spoken it, and I will do it is stated because it is said: And God remembered Sarah as He has said, and the Lord did unto Sarah as He had spoken (ibid. 21:1).

Sarah conceived on Rosh Hashanah, and Isaac was born in the seventh month, on the night of Passover, as is said: I will certainly return unto thee when the season cometh around (Gen. 18:10). Four barren women conceived on Rosh Hashanah: Sarah, Rebecca, Rachel, and Leah.